UNIT 23 - MONOCOT FAMILIES Structure I~itroduction 0b.jectives Musaceae Lil iaceae Arecaceae Poaceae Summary Terminal Questio~is Answers 23.1 INTRODUCTION The non no cotyledons constitute one of the two major groups of angiosper~ns. They are rnostly lierbaceo~isplants. Tlie stems liave closed vascular bundles. Due to the absence of vasc~~larca~nbium, tliese plants do not exhibit normal secondary growth as observed in tlie dicotyledo~iswliicli you have already read in Unit 8 of Block I1 of Develop~iientalBiology, LSE-06. T-lowever, a few monocotyledons are woody and have tree-like stems je.g., barnboos and palms). The leaves generally liave a basal sheath and sliow parallel venation. Tlie flowers liave a cliaracteristic trinierol~sorganisation. Tlie enibryo rarely sliows differentiation and lias a single (hence the lialiie mono) cotyledon. 'l'lie e~idospertiiis ~~sually abundant. Tlie monocotyledons are comparatively fewer tlian the dicotyledons. TIiey are classified into 7 series and 34 families in 13entliarn and Hooker's classification. In this system, tlie ~nonocotyledo~isare classified after tlie dicotyledons. In contrast to tliis, they are classified before the dicotyledo~isin Engler & Prantl's System. A total of 1 1 orders and 34 fa~iiiliesare recognised in tliis system. Taklitajan in his system of classification (as revised in 1997) has classified tlie mo~iocotyledonsin class Liliopsida. This is placed after class Mag~ioliopsida(= dicotyledons), l'he Liliopsida is divided into 6 subclasses, 16 super orders, 57 orders and 13 1 families. In this unit yo11 will study about the characters of 4 important monocot families. These are Musaceae, Liliaceae, Arecaceae (Palmae) and Poaceae (Grarnineae). l'liis study follows tlie same pattern as in tlie case of tlie dicotyledon families dealt with in ~uiits2 1 arid 22. Objectives AAer studying 1:Iiis unit, you should be able to: @ know about the families Musaceae, Liliaceae, Arecaceae and Poaceae. remember tlie ~iolnenclaturaltype of each family name. @ know about tlie size, distributio~ias well as tlie number of genera and species of tliese families foulid in India. @ understand the morphological diversity in eacli family. list tlie diagnostic features of eacli fa~nilya~id recognise tlie plants in the field. @ classify each family in 3 systerns of classification and know its systematic position. @ list the eco~io~nicallyi~nportatit platits and know about their uses. The Banana family Nomenclatural Type: Musn Gerieral Information This is a ve~ys~nall family of ~nonocotyledono~~splants. Tliere are two views on tlie number of genera and species in this family. Engler and Prantl classified 6 genera in this family. Tliese are Musa (about 80 species incliiding Ensete); Ravenala (25 species); Strelitzia (4 species); Heliconirr (30 species); Lowia (2 species); and Orchidantha (2 species). On the other hand, taxonomists like Taklitajan, Hutcliiriso~iand C~~onquist recognise only 2 genera - Mtrsa (about 60 species) and Ensetc (about 20 species). ?'lie other genera are classified in Strelitziaceae (Raverzala and Strelitzia); Heliconiaceae (genus Heliconia) or Lowiaceae (Orchidantha including Lowia). ' This difference in the size of tho famiiy Musaceae in different systems of classification is mainly due to the morphological diversity amongst tlie plants. Therefore, it would be more appropriate to know about this diversity and follow tlie suggestion of Engler & Prantl. In this context of tlie family Musaceae you should remember two terms; sensu strict0 and sensu lato. These were introduced to you in LSE-07, Block 2, Unit 7. Therefore, the following discussion describes tlie fa~niIyMusaceae sensu lato, Tlie members of this family are tropical in distribution. They are found in Asia, Africa and South America. However, there is a large-scale cultivatio~iof tlie economically important genus Musa throughout tlie warmer parts of tlie world. Ravenala, Strelitzin and Helicoiiia are cultivated in parks and gardens as ornamentals. Ficld Recognition Herbaceous perennials with "tree like" pseudoste~iisor woody palm-like plants; leaves large with oblong blade having a distinct slieatli, a stout midrib and parallel venation; illflorescence with characteristic spathe-like bracts; flowers zygomorphic and generally unisexual; male flowers usually with five stamens and one staminode; female flowers with tricarpellary gynoeciu~nand inferior ovary. Morphological Diversity The plants of the family Musaceae are generally perennial herbs with an underground rliizome. In the largest genus Musa, an aerial pseudostein (growing up to a height of 5 meters) is formed. This is actually made up of large stiff leaf slieaths which are rolled around ane another. "Tllerefore, it is not a true stem. The true stem is the underground rl~izorne,the apex of which is present at tlie base of the pseudostem. The rhizomatous stern grows out tlirough the cylindrical pseudostelm to bear the terminal inflorescence. Tlie plants are herbaceous perennials in Lowia, Orchidantha and Strelitzia reginae (called Bird of Paradise) also. But Strelitzia nicolai and Ravenala madagascarie~sis(cal led Traveller's tree of Madagascar), are tall woody trees with a palm-like appearance, Leaf: In Musa, tlie leaves are arranged radially in two rows on tlie riiizome. This pattern of leaf arrangement also occurs in the other herbaceous perennials. In Musu, the leaves appear to arise at the apex of tlie pseudostem (Fig. 23.1). T11is is due to th'e fact that the leaf sheaths are rolled around one another and each new leaf pushes up 1 its convolute blade through the pseudostern. The large blade then expands above the, older leaves. In the woody plants like Rmenala, the leaves are arranged in two rows, forming a crowded crow11 at the apex of the trunk (Fig. 23.2). I I Monocot Families Fig. 23.1: Musn sp. a) Young plant. b) nese of olrnt with s~~cket~.c) Inflorcsccncc. d) Pcmnlc flowers and bract. c) Mnlc flowcrs and brrct. f) Felnnlc flower. g) Fcnlnle flower wit11 pcrinntll opcnecl. 11) Fcmale flower ill longitl~dinrlscction. i) blz~lcIlowcr. j) ~III~Cflowcr wit11 pcrianth opcncd. k) Mnle flower ie longitudinal section. I) Fruit bunch Families of Angiosperms Fig. 23.2: R~venalamadogascoriensis.a) Plant in flowering stnge. b) Open flower. c) Opening cnpsule. ' dl Seed with aril. The leaves are large and consist of a strong sheath wliicl~is separated from tlie oval or oblong blade. The blade has a thick midrib from which numerous parallel veins travel to the margins. There is no a~lastomosisof the seco~idaryveins (common in dicots), so that the edges of the large blade easily split. Mature leaves are generally torn up to the midrib thus offering very little resistance to wind forces. In Ravenala rnadagascnriensis (Traveller's tree), water accunlulates in the leaf base. This water has been used for drinlting purposes by travellers. Inflorescence: The infloresce~lceis terminal in Musn: It is a large racemose inflorescence having numerous large bracts. The bracts are spathe-like and brightly coloured. Each bract encloses a large number of unisexual flowers. The flowers towards the apex of the inflorescence are male, while those towards the base are female. Sometimes bisexual flowers may be present in the middle region of the inflorescence. In Heliconia (Fig. 23.3) the ter~ni~ialinflorescence has 2 rows of large bracts. In the axil of each bract, there is a rnonochasial cyme of the cincinnus type. Ravenala and Sfrelitzia have several axilliary i~iflorescenceswith large bracts. Each bract has a cincin~lustype of tnonocliasial cyme with many (Ravenala) or few (Strelitzia)flowers. In Lowia and Orchidantha, the inflorescence is a panicle with large orchid-like flowers. Flower: The flowers are bracteate, zygomorphic and bisexual in their ontogeny, They become unisexual because either the androeciuni 01- the gynoeciu~ndoes not mature. They are trimerous as in other monocotyledo~lsand they are epigynous. The perianth of the flower consists of two trimerous wllorls and the six tepals arc generally petaloid. The perianth may also be distinguished into a distinct calyx and corolla. In Musa, the 3 outer and 2 inner tepals are united to form a tube, while the sixth is free. They are unequal in size and the inner tepals are smaller and narrower than the outer. In Ravenala, tlie 2 whorls of the periantli show a differentiation into a calyx and corolla. One (median) petal is slightly smaller than all other segments of the perianth. Strelitzia has free sepals while 2 lateral +t?l~ are w;iidd to form a lar e broadly winged arrow shaped structure which Monocot Families surrounds the stamens. The 3' 9 or odd petal is very short and broad. In Lowia and Orchidantha (Fig. 23.4), the sepals are unitedhto a cup-like structure. The two L. lateral petals are small while the third forms a large spreading labellum. In these genera, the flowers show resupination (this is a change in the orientation of the flower caused by a twist in some portion of the flower axis. This results in the posterior portion of the flower to appear anterior and vice-versa). This is a com~nonfeature in the family Orchidaceae. Fig. 23.3: Heliconinsolomonensb.a) Inflorescence, notc pollinntlng ~nncroglossinehat. b) Clncinnnl bract cut away to sl~owflower at anthcsis. c) Ovary wlth style, stigma, and staminode. d) Stnminode. e) Pyrenes in ventral and lateral view. Androecium: There are two trimerous whorls of stamens in each flower. All six .stamens are fertile and of equal size in Ravenala. In some species of Musa (e.g., M ensete), 5 stamens are large and tlie sixth one and is small, but in all the other genera, only 5 stamens are fertile and the sixth stamen is reduced to a starninode. This staminode becomes petaloid in Heliconin and it is completely suppressed in Lowia and Orchidantha. The anthers are linear, dithecous and show introrse dehiscence. A rudimentary ovary which is generally modified into a nectary is usually present in the male flowers.